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Biology Day 1 Microscope and Units of Measurement Units of Measurement: Scientists use special units to measure and describe the size of cells and particles too small to be seen with the naked eye. The commonly used units in the study of microscopic objects are outlined in the table below. Unit Equivalent Measurement 1/100 meter Centimeter (cm) (100 cm to 1 m) 0.01 m Millimeter (mm) Useful in Observing Visible objects 1/10 centimeter (10mm to 1 cm) Large particles or cells 0.001 m 1/1000 millimeter Micrometer (um) (1000 um to 1mm) (aka. Micron) 0.000001 m Majority of cells and their parts (inside the cell) 1/1000 micrometer Nanometer (nm) (1000nm to 1 um) 0.000000001 m Large molecules and most cell parts Angstrom (Ǻ) 1/10 nanometer (10 Ǻ to 1nm) 0.0000000001 m Molecules and atoms 1mm = 1000 μm 1 cm = 10,000 μm Converting between units: Example: 240 μm is equivalent to how many mm? Example: How many millimeters is 25 centimeters? Example: 2 cm is equivalent to how many micrometers? Questions: 1. How many micrometers are in 1 millimeter? 2. Convert: a. 6.5 mm = μm b. 7.2 cm = μm c. 1500 μm = mm d. 65 μm = mm 3. A frogs egg is 1mm across. If an E.coli bacteria is 2.0 μm in length, how many would fit across the frogs egg? 4. A penny measures 1 cm across. How many E.coli could fit across a penny? . 1 Compound Light Microscope: Refer to Student Reference 8 (pg. 478481) for help. The compound light microscope magnifies objects placed very close to the objective lens. The microscope you will be using has 3 objective lenses positioned on a revolving nosepiece. The objective lenses will be labeled 4x, 10x and 40x. The shortest will be the smallest magnification objective lens (4x) and the longest will be the highest magnification objective lens (40x). Some research microscopes (very expensive) have 100x objective lenses. The objective lens clicks in place. Each objective lens is made up of two lenses. The specimen, on a glass slide covered with a thin coverslip, is placed on the moveable microscope stage close to the objective lens. The slide is held in place using the stage clips. Begin with the lowest power objective lens in position over the slide. The objective lens should never touch the slide. The stage can be moved up or down using the coarse adjustment knob. Watching from the side, bring the lowpower objective as low as possible by using the coarse adjustment knob. You are able to observe the specimen by looking through the eye piece or ocular lens. The eyepiece is labeled with the magnification it provides, usually 10x. Look through the eyepiece and bring the specimen into view by using the coarse adjustment knob. Then produce a clear, sharp image using the fine adjustment knob. Below the stage is the diaphragm that adjusts the diameter of an opening to control the amount of light passing through the specimen. The lamp at the bottom of the microscope supplies the light required to view the specimen. Sometimes, a mirror is present instead of a lamp and is used to direct light from the surroundings through the diaphragm. Microscopes are sensitive and expensive pieces of lab equipment and require careful care, storage and handling. When moving the microscope, remember to hold the arm with one hand and support the weight of the microscope under the base with the other hand. The microscope should always be stored with the lowpower objective lens in position. 2 3 Fill in the chart on the function of each part of the compound microscope: Microscope Part Function Contains ocular lens Eyepiece or Ocular Lens Magnifies 10X Coarse Adjustment Knob Approximate resolution on image Fine Adjustment Knob Clear, sharp resolution on image Rotates Revolving Nosepiece Holds the 3 objective lenses Objective Lenses Magnifies Low power 4X Medium power 10X High power 40X Platform Stage Stage Clips Has Condenser lens that gathers light to a fine point Hold the slide in place Rotating disc that has circles of differ diameter Diaphragm Allows for diff amounts of light to get through Lamp or Mirror Electrical light bulb that is the light source Arm Provides a handle to carry the microscope by Base Hold microscope together 4
